Conventionally, effect adding apparatus are known which add various effects such as reverberation/delay to musical note waveforms fed from a sound source of an electronic musical instrument to produce effect sounds.
Recently, as the sound sources of such apparatus become multi-timbres oriented, the apparatus have come to include a digital signal processor (DSP) which processes at high speeds musical note waveforms of different timbres produced simultaneously by the sound source so that a plurality of different effects are added in common to the note waveforms or effects different in timbre are added to the note waveforms.
In such effect adding apparatus, the number of effect types to be added simultaneously is determined depending on the processing ability of the DSP. That is, in the conventional apparatus, effects assigned for each timbre cannot change during operation of the apparatus and are assigned as fixed, so that the sum of calculation times of the DSP required for processing the respective effects assigned to a respective one of note producing channels of the sound source can exceed one sampling period of the note waveform. In this case, real time effect addition cannot be performed and the number of different effects which can be added simultaneously is limited.
For example, when there can be a limitation that "chorus" and "distortion" effects cannot be added simultaneously, "chorus" cannot add to a string note while "distortion" to a guitar note being added, which limits a type of addition of the musical effect.